Antiestrogen and antiprolactin drugs have been studied in women with stage IV breast cancer with the hope of developing a "medical hypophysectomy." The antiestrogen drug, Tamoxifen, has yielded and incidence and duration of remission which is approaching and may exceed that of surgical hypophysectomy. Furthermore, Tamoxifen has induced remissions in women who had previously responded to "complete" surgical hypophysectomy, thus yielding additional palliation not previously possible. An effective antiprolactin drug has yielded only minor antitumor effects in women with breast cancer, suggesting that prolactin plays a less important role than estrogens in stimulating tumor growth. However, hypophysectomy has induced further remissions in women who were previously treated with antiestrogens, suggesting that pituitary hormones are playing a role in stimulating tumor growth in some patients. Since human growth hormone is known to have lactogenic properties, it may be that suppression of growth hormone and prolactin is needed for optimal antitumor effects. A drug to inhibit growth hormone secretion is under investigation. It seems possible that a combination of antiestrogen, antiprolactin and antigrowth hormone drugs might yield an optimal form of medical treatment for hormone responsive breast cancer. Estrogen, progesterone and prolactin receptors are being measured in tumor tissue to determine whether multiple receptors will enhance the predictability of hormone responsiveness. Optimal endocrine therapy will be combined with optimal cytotoxic chemotherapy in patients with metastatic disease to determine whether this will be more effective than sequential therapies. A prospective, randomized study of adjuvant endocrine therapy, cytotoxic chemotherapy and immunotherapy for patients with stage II primary breast cancer is underway to determine whether early systemic treatment when the tumor burden is lower may produce "cures" or prolonged survival free of detectable disease.